Question: A board game spinner is divided into three regions labeled $A$, $B$ and $C$.  The probability of the arrow stopping on region $A$ is $\frac{1}{2}$ and on region $B$ is $\frac{1}{5}$.  What is the probability of the arrow stopping on region $C$?  Express your answer as a common fraction.
Explanation: Since the sum of the three probabilities is 1, the probability of stopping on region $C$ is $1 - \frac{1}{2} -
\frac{1}{5} = \frac{10}{10} - \frac{5}{10} - \frac{2}{10} = \boxed{\frac{3}{10}}$.